The embodiments disclosed herein relate generally to methods and devices used to enhance the quality of images of objects in obscured environments. It is known in the art that photonic detectors have a dynamic range that is much less than the range of light levels that are directed onto them in typical optical imager applications. It is standard practice to use gain control to set the sensitivity of the detectors based on the brightest light levels being detected. This involves the use of an electronic processor to analyze the signals generated by the detectors and to adjust the detector sensitivities to achieve a discernible response to a particular average signal level from an ensemble of detectors. Once the electronic gain has been set, this determines the minimum light level signal to which the detectors will respond. For this gain setting, variations in the scene light levels below this minimum are not detectable.
Selecting pass band filters to increase signal to background clutter ratios, taking advantage of known detector types and the exploitation of available optical materials are known in the art. Popular electromagnetic pass bands such as those referred to as visible (VIS), near-infrared (NIR), and thermal have become standards in industry. System components based on these standards are commonly available and are widely used in the development of non-imaging and imaging electro-optical systems. In common practice other pass bands have been overlooked or actively avoided due to the presence of absorption bands by atmospheric constituents such as O2, NO2 and H2O. Pass band filters, optical systems and detectors are designed to utilize spectral regions that exclude these absorption bands. A typical use of a pass-band filter might be to block unwanted bands, thereby making it easier to amplify a desired band or bands. The embodiments disclosed herein do not work this way. Instead, the embodiments disclosed herein take advantage of the fact that the H2O absorption band (e.g. fog) admittedly blocks some light, but also absorbs other portions of scattered light. The embodiments disclosed herein focus on taking advantage of these absorbed portions, in order to more effectively view an image in an environment where fog is present.